This invention relates to a seam-tracking apparatus for a welding system and, more particularly, the present invention relates to a seam-tracking apparatus employing an eddy current sensor array.
In automated welding processes, it is desirable to be able to continuously and automatically control the positioning of a welding arm advancing relative to a weld seam. For instance, the quality of the weld joint depends to a large extent on how precisely an energy beam directed from the advancing welding arm is continuously centered or aligned relative to the seam. Such precise alignment becomes even more critical in applications wherein the beam of energy is highly concentrated over a narrow beam having a submillimeter radius dimension, as is typically the case in welding systems which use laser or electron beams or the like.
Several different forms of seam-tracking devices have been proposed to guide automated welding systems, included among such devices are industrial vision systems using TV cameras, optical sensors using a scanning laser beam for scanning the surfaces of the workpieces to be welded, and infrared sensors.
Although impressive improvements have been made in such seam-tracking devices, significant disadvantages remain. For example, the sensitivity, dynamic range and background rejection capabilities of vision systems using TV cameras generally do not permit reliable tracking of a tightly spaced seam between a pair of closely abutting workpieces to be welded. Devices using a scanning laser beam may require a relatively powerful laser to overcome variations in surface reflectivity, thus necessitating special safety precautions which are economically disadvantageous and operationally cumbersome. In the case of seam-tracking devices which employ infrared sensors, the use of infrared filters to block out extraneous infrared radiation is ordinarily required. The need of such filters adds to the cost as well as to the complexity of such infrared seam-trackers.
Eddy current sensors have also been proposed for seam-tracking devices. However, eddy current seam-tracking devices of the kind proposed heretofore, in general, lack both the resolution and accuracy detection capability required for precisely tracking tightly joined seams. Moreover, eddy current seam-tracking devices proposed heretofore have usually employed essentially inflexible eddy current sensors which, as may be expected, cannot conform to an arbitrary surface geometry in the workpieces to be welded, thereby such seam-tracking devices have had limited applications in welding operations in which the workpieces to be welded have significantly curved surfaces. In addition, eddy current seam-tracking devices proposed heretofore have commonly used eddy current sensors comprising a single sense element which has not been able to provide the resolution and sensitivity required to accurately and precisely track a tight seam having a rapidly varying curvature in an arbitrarily configured workpiece surface, thereby having limited applications in welding operations wherein the seam to be tracked is not substantially straight.